C中的fscanf csv未分配值
我试图创建一个文件来读取包含CSV的文本文件。 但是出于某种原因,一些Fscanfs不会返回值,但有些值会返回。
FILE* reader; char OptionOne[30]=""; char OptionTwo[30]=""; char OptionThree[30]=""; char OptionFour[30]=""; char answer[1]=""; char CorrectAnswer[1]; char Question[51]; reader = fopen("C:\\Users\\Finley\\Desktop\\Programming\\QuizMachine\\QuizMachine\\fscanf_questions.txt", "r"); if (reader == NULL) { printf("Unable to Open File: %s\n", FileName); } fscanf(reader, "%[^,],", Question); fscanf(reader, "%[^,],", OptionOne); fscanf(reader, "%[^,],", OptionTwo); fscanf(reader, "%[^,],", OptionThree); fscanf(reader, "%[^,],", OptionFour); fscanf(reader, "%[^,],", answer);
为什么第一个fscanf返回一个值,但所有其他值都没有返回值。 我看不到任何东西,它们看起来都是一样的同样的格式文件格式是这样的:
你用什么函数打开文件?,fscanf,fclose,fopen,main,3
以下哪一项不是变量类型?,int,float,char,string,4
-
需要使用足够大小的缓冲区。 答案,作为一个字符串需要至少2个
char
。 @Daniel -
fscanf()
应限制输入以防止缓冲区损坏。 宽度说明符通常比缓冲区的大小小1。char Question[51]; fscanf(reader, "%50[^,],", Question);
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应检查
fscanf()
的结果。if (fscanf(reader, "%50[^,],%29[^,],%29[^,],%29[^,],%29[^,],%1s", Question, OptionOne, OptionTwo, OptionThree, OptionFour, answer) != 6) { Handle_Bad_input(); }
-
如果输入没有跟随
','
,请不要使用"%[^,]"
作为最后一个值,否则fscanf()
将读取下一行。 -
建议使用空格来引导每个
"[^,]"
以跳过前导空白区域。if (fscanf(reader, " %50[^,], %29[^,], %29[^,], %29[^,], %29[^,],%1s",
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更好:用
fgets()
读取行 ,然后扫描缓冲区。char buf[200]; if (fgets(buf, sizeof buf, reader) == NULL) Handle_IOErrorOrEOF(); if (sscanf(buffer, "%50[^,],%29[^,],%29[^,],%29[^,],%29[^,],%1s", Question, OptionOne, OptionTwo, OptionThree, OptionFour, answer) != 6) { Handle_Bad_input(); }
你的answer
缓冲区太小,所以fscanf
写的太多,导致腐败。
你给它的大小只有一个字符,但是fscanf
会在其中写入两个字符:你想要的字符,3和空字符\0
。
将缓冲区大小增加到2可以解决问题。
this line: fscanf(reader, "%[^,],", Question); (and those like it) have a couple of problems. 1) should always check the returned value from a input I/O statement to assure the conversion was successful 2) the format string is missing the type conversion, in this case 's' this line: fscanf(reader, "%[^,],", answer); will fail if the line does not end in a ',' "Why does the first fscanf return a value but all the others not return a value." ans: 1) because the ' ' after the comma is not consumed 2) use a leading ' ' in the format strings to consume white space this will also consume an trailing '\n' on each line 3) a type specifier is NOT optional in a format string, use 's' 3a) I would have read in the 'answer' as a char using '%c' for a format conversion and only created a char, not a char array. 4) to avoid buffer overruns, include the 'size-1' optional part of each format conversion, just in case some string length is = or greater than the receiving buffer "I cannot see anything and they all seem the same with the same formating File formatting is like this:" ans: where is the file formatting info? this line: printf("Unable to Open File: %s\n", FileName); the variable FileName is not set. suggest setting char * FileName = C:\\Users\\Finley\\Desktop\\Programming\\QuizMachine\\QuizMachine\\fscanf_questions.txt" and using 'FileName' in the fopen() statement. this line: printf("Unable to Open File: %s\n", FileName); after this line, should insert 'exit(EXIT_FAILURE); rather than continue in the program, trying to use that NULL file descriptor pointer this line: char answer[1]=""; will be a problem as the input is being read in as strings, so even for a single char string, there still needs to be room for the trailing '\0' this line: fscanf(reader, "%[^,],", answer); 1) fails if each line of the input file, including the last line, does not end in ','